1. Field of the Invention
The present invention relates to a backlight device and particularly to an edge light type backlight device for use in a liquid crystal display (LCD) or the like.
2. Description of Related Art
A liquid crystal display device is widely used in note book computers or portable TVs and generally comprises a liquid crystal panel and a backlight system to provide uniform collimated light to the liquid crystal panel. The backlight system mainly comprises a light source and a light guide plate. The light guide plate is made of a transparent acrylic resin and is used for guiding the light beams emitted by the light source to uniformly illuminate the liquid crystal panel.
Referring to FIG. 11, U.S. Pat. No. 6,443,583 discloses a backlight system 1. The backlight system 1 includes a light source 110, a light source cover 120 and a light guide plate 200. The light guide plate 200 comprises a light input surface 201, a light output surface 203 adjoining the light input surface 201 and a bottom surface 202 opposite to the light output surface 203. The backlight system 1 further comprises a reflective sheet 210 opposite to the bottom surface 202, a diffusion sheet 220 opposite to the light output surface 203, a prism sheet 230 disposed above the diffusion sheet 220 and a protecting film 240 disposed above the prism sheet 230.
In operation, the light source 110 emits light beams and the light beams are transmitted into the light guide plate 200. The reflective sheet 210 reflects the light beams and directs the light beams to exit from the light output surface 203. The light beams then sequentially pass through the diffusion sheet 220, the prism sheet 230 and the protecting film 240 to illuminate a liquid crystal panel.
However, the conventional backlight system 1 has some disadvantages. First, the backlight system 1 comprises a plurality of optical elements, such as the reflective sheet 210, the diffusion sheet 220, the prism sheet 230 and the protecting film 240, which makes it high in manufacturing cost and complicated in structure. Second, a large amount of the light beams generated by the light source 110 is usually lost after passing through the optical elements of the backlight system 1.
Therefore, an improved backlight system which overcomes the above-described disadvantages of the conventional backlight system is desired.